Cross-correlation of galaxies and galaxy clusters in the Sloan Digital Sky Survey and the importance of non-Poissonian shot noise

Abstract

We present measurements of angular cross power spectra between galaxies and optically-selected galaxy clusters in the final photometric sample of the Sloan Digital Sky Survey (SDSS). We measure the auto- and cross-correlations between galaxy and cluster samples, from which we extract the effective biases and study the shot noise properties. We model the non-Poissonian shot noise by introducing an effective number density of tracers and fit for this quantity. We find that we can only describe the cross-correlation of galaxies and galaxy clusters, as well as the auto-correlation of galaxy clusters, on the relevant scales using a non-Poissonian shot noise contribution. The values of effective bias we finally measure for a volume-limited sample are $b_{cc}=4.09 \pm 0.47$ for the cluster auto-correlation and $b_{gc}=2.15 \pm 0.09$ for the galaxy-cluster cross-correlation. We find that these results are consistent with expectations from the auto-correlations of galaxies and clusters and are in good agreement with previous studies. The main result is two-fold: firstly we provide a measurement of the cross-correlation of galaxies and clusters, which can be used for further cosmological analysis, and secondly we describe an effective treatment of the shot noise.